KR20200041900A - Method for stabilizing aqueous dispersions of fluorinated polymers - Google Patents

Abstract

The present invention relates to methods for stabilizing aqueous dispersions, in particular aqueous dispersions of polymers based on vinylidene fluoride (VDF), and their use in the electrochemical applications of the stabilized aqueous dispersions thus obtained.

Description

Method for stabilizing aqueous dispersions of fluorinated polymers

Cross-reference with related applications

This application claims priority to European application EP 17185838.4, filed on August 11, 2017, the entire contents of which are incorporated herein by reference for all purposes.

Technology field

The present invention relates to methods for stabilizing aqueous dispersions, in particular aqueous dispersions of polymers based on vinylidene fluoride (VDF), and their use in the electrochemical applications of the stabilized aqueous dispersions thus obtained.

Aqueous dispersions of fluoropolymers and their applications are well known in the art.

For example, US 20020193500 (3M INNOVATIVE PROPERTIES COMPANY) discloses a method for preparing a fluoroelastomer latex, the method comprising (A) copolymerizing to form an aqueous emulsion of monomers capable of forming a fluoroelastomer. ; (B) polymerizing the emulsion at a temperature of about 40 ° C to 130 ° C and a pressure of about 2 to 9 MPa to form a fluoroelastomer emulsion composition; (C) adjusting the pH of the fluoroelastomer emulsion composition to 5-9 by adding a sufficient amount of base; And (D) concentrating the fluoroelastomer emulsion composition having a pH of 5 to 9 to form a solid-rich fluoroelastomer latex. The emulsion of step (A) comprises a first monomer selected from vinylidene fluoride (VDF) and tetrafluoroethylene (TFE), at least one other fluorine-containing monomer, free radical initiator, fluorinated surfactant and base. Includes. After preparation of the fluoroelastomer emulsion composition, its pH is adjusted by adding a base. The pH of the polymerization reaction mixture should be maintained in the range of 3 to 8, preferably 5 to 8.

This patent application lists some fluorinated surfactants suitable for use during step (A), as well as fluorinated and non-fluorinated surfactants suitable for further stabilizing the composition. However, this patent application only discloses fluoroelastomers, ie fluoro-carbon based synthetic rubbers, and does not mention anything about semi-crystalline polymers. Moreover, this patent application does not directly address the problem of providing latex suitable for use in battery applications, and does not provide any hints for the selection of surfactants for this particular application.

Similarly, EP 1897902 A (DAIKIN IND LTD) (12/03/2008) discloses a method for producing an aqueous fluoropolymer dispersion, the method comprising the use of a nonionic surfactant in an aqueous fluoropolymer dispersion to be treated. Step (1) of adding, phase separation of the supernatant phase and the aqueous fluoropolymer dispersion phase after step (1) (2), and recovering the aqueous fluoropolymer dispersion phase by removing the supernatant phase ( 3), in step (2) stirring is provided. According to this document, the addition of the nonionic surfactant can be carried out after adjusting the aqueous fluoropolymer dispersion to be treated to pH 3 to 12 using, for example, aqueous ammonia solution. Among fluoropolymers, VDF-based polymers (eg, VDF / HFP copolymer, VDF / chlorotrifluoroethylene [CTFE] copolymer, VDF / TFE copolymer, VDF / perfluoro (alkyl vinyl ether) [PAVE ] Copolymers, VDF / TFE / HFP copolymers, VDF / TFE / CTFE copolymers and VDF / TFE / PAVE copolymers).

US 20100304270 (ARKEMA INC.) Discloses an aqueous fluoropolymer, preferably polyvinylidene fluoride (PVDF) composition for making electrodes for use in non-aqueous-type electrochemical devices, such as batteries and electric double layer capacitors do. The composition contains an aqueous PVDF binder, and one or more powdered electrode-forming materials.

Vinylidene fluoride (VDF) polymers are binders for the production of electrodes and / or composite separators for use in non-aqueous-type electrochemical devices, such as batteries, preferably secondary batteries, and electrical double layer capacitors. , And / or suitable as a coating material for porous separators are known in the art.

In this field, in particular, the ability to provide agglomeration of electrode active materials and / or composite separators with inorganic fillers, the ability to ensure adhesion to metal collectors, separator porous substrates, stability / non-solution to liquid electrolyte solutions, and electricity All the properties required for use in the field of secondary battery components, including the prevention of contamination by chemicals that are likely to interfere with the chemical reaction (e.g., fluorosurfactants with insufficient electrochemical stability). Having this, there is still a continuing need for aqueous dispersions of VDF polymers with suitable properties for processing, including shear stability during formulation and casting, and acceptable shelf life.

Now, the technique of making VDF dispersions is usually based on the polymerization of aqueous emulsions in the presence of fluorinated emulsifiers, which are generally difficult to remove from the resulting dispersion, and as a contaminant to electrochemical device parts. It can have harmful effects. Attempts to reduce or even eliminate fluorosurfactants in the emulsion polymerization of VDF to provide stable VDF polymer dispersions that do not contain fluorosurfactants are known, but such a technique allows the polymerization of polymer rings through end group chemistry. It is understood to be based on self-stabilization. Increasing molecular weight will reduce the overall concentration of the ring ends, thus leading to a lack of stabilization.

US 5880204 (ALLIED SIGNAL INC) discloses a room temperature coalesceable aqueous fluoropolymer dispersion, the dispersion comprising particles of a block copolymer having a first semi-crystalline block and a second amorphous block. The first and second blocks are generally VDF or CTFE copolymers, the second block generally comprises a so-called “curing-site provider”, and the curing-site provider can be particularly an acid, such as acrylic acid. In general, fluoropolymers generally have an Mw of 10,000 to 1,000,000 (and thus range from low molecular weight to ultra high molecular weight). These dispersions are taught to be useful as floor polish. Generally, latexes are prepared in the absence of surfactants, using redox initiation systems at relatively low polymerization temperatures.

WO 2013/010936 (SOLVAY SPECIALTY POLYMERS ITALY SPA) relates to an aqueous composition, the aqueous composition comprising (A) vinylidene fluoride (VDF) and at least one (meth) acrylic monomer (MA) (preferably acrylic acid) (AA) an aqueous latex comprising at least one vinylidene fluoride (VDF) polymer (polymer (F)) comprising a repeating unit derived from (B) at least one powdered electrode material, and (C) ) Optionally, less than 10% by weight of at least one organic solvent (S) based on the total weight of the aqueous composition, wherein the polymer (F) in the aqueous latex has an average primary particle size as measured according to ISO 13321. It is in the form of primary particles less than 1 μm. This document also describes a method for making an electrode using the aqueous composition, an electrode comprising a metal substrate coated on at least one surface with the aqueous composition, and the use of the electrode for making a non-aqueous-type electrochemical device It is about. These latexes are prepared by aqueous emulsion polymerization at a pressure of 20 bar to 70 bar and a temperature of 60 ° C to 135 ° C, preferably 90 ° C to 130 ° C in the presence of a micro-emulsion or fluorosurfactant.

WO 2015/059155 (SOLVAY SA) relates to an electrode-forming composition, the electrode-forming composition comprising (a) vinylidene fluoride (VDF), at least one hydrogenated monomer (preferably AA), and optional An aqueous latex comprising at least one fluoropolymer [polymer (F)] comprising repeating units derived from at least one other fluorinated monomer that is different from VDF and homogeneously dispersed therein, (b) sulfur Consisting of at least one powdered electrode-forming material, (c) at least one powdered electrically conductive material, wherein the polymer (F) in the aqueous latex has an average primary particle size of 1 as measured according to ISO 13321. It is in the form of primary particles less than μm. This document also relates to the use of the composition in the method of making the composition and in the method for producing the positive electrode for a lithium-sulfur battery. These latexes are prepared by aqueous emulsion polymerization, possibly at a pressure of 20 bar to 70 bar and a temperature of 60 ° C to 135 ° C, preferably 90 ° C to 130 ° C, in the presence of a micro-emulsion or fluorosurfactant. .

WO 2008/129041 (SOLVAY SOLEXIS SPA) is a linear semicrystalline copolymer comprising repeat units derived from at least one hydrophilic (meth) acrylic monomer and vinylidene fluoride (VDF) monomer statistically distributed in a polymer ring, And a method for its preparation by suspension polymerization in combination with the stepwise addition of acrylic monomers.

WO 2013/120858 (SOLVAY SPECIALTY POLYMERS ITALY SPA) relates to a method of manufacturing a composite separator for an electrochemical cell, the method comprising

(i) providing a substrate layer;

(ii)-an aqueous latex comprising at least one VDF polymer latex, and

-At least one non-electroactive inorganic filler material

Providing a coating composition comprising a;

(iii) applying the coating composition on at least one surface of the substrate layer to provide a coating composition layer; And

(iv) drying the coating composition layer

It includes.

WO 2014/095907 (SOLVAY SPECIALTY POLYMERS ITALY SPA) relates to a method for producing a dense film, the method comprising the steps of providing a solid composition of a VDF fluoropolymer comprising at least one PAO and a carboxyl group; And processing the mixture in a molten phase to provide a high density film, which can be used as a high density separator in an electrochemical device.

However, the above mentioned documents do not specifically address the problem of stabilizing fluoropolymer dispersions.

Applicants have continued in the art for aqueous dispersions of vinylidene fluoride (VDF) -based polymers with improved performance in lithium battery applications while still having substantial latex stability to provide adequate shelf life and processability. It was recognized that there was a defect.

Surprisingly, the Applicant has discovered that the problem includes a first step of adjusting the pH of the aqueous dispersion of the VDF-based polymer to a value above 6.5 and a second step of adding a nonionic surfactant comprising a primary alcohol group. It can be solved by.

Thus, in a first aspect, the present invention is for stabilizing an aqueous dispersion [dispersion (D _a )] comprising particles of a (semi) crystalline VDF-based polymer [polymer (F)] comprising the following steps: How to:

(I) providing the dispersion (D _a );

(II) contacting the dispersion (D _a ) with at least one base to provide a VDF-based (semi) crystalline polymer aqueous dispersion having a pH above 6.5 and below 9.0 (dispersion (D _b )). ;

(III) The dispersion (D _b ) obtained in step (II) comprises a hydrogenated linear alkyl chain containing 6 to 15 carbon atoms and a (poly) alkoxylation group containing 2 or 3 carbon atoms. Contacting at least one nonionic surfactant (compound (S)) to provide a stabilized aqueous dispersion [dispersion (D _F )].

Surprisingly, the Applicants may arise from base-induced side reactions, while the method according to the method, including the step of adjusting the pH within a very precise range, demonstrates excellent behavior in the field of use of electrochemical cell components. Aqueous dispersions that have sufficient stability to coagulation and are not adversely affected by base addition, to ensure adequate shelf life and processability in the absence of fluorinated surfactants, while avoiding the presence of contaminants such as fluoride ions. I found that it makes it possible to generate.

In a second aspect, the invention relates to a VDF-based (semi) crystalline polymer aqueous dispersion obtained by the above-mentioned method [dispersion (D _F )].

As used within this specification and in the following claims,

-The expression "(semi) crystalline polymer" has a heat of fusion greater than 1 J / g, more preferably when measured by differential scanning calorimetry (DSC) at a heating rate of 10 ° / min according to ASTM D-3418. 35 J / g to 1 J / g, even more preferably 15 to 5 J / g;

-The term "dispersion (D)" is intended to denote dispersion (D _a ), dispersion (D _b ) and dispersion (D _F ), respectively, unless otherwise specified;

-The term "dispersion (D)" is intended to denote an aqueous dispersion comprising particles of at least one polymer (F), the particles having an average size of less than 1 μm as measured according to ISO 13321, Accordingly, the terms "dispersion (D)" and "latex" are intended as synonyms.

According to a preferred embodiment, the compound (S) is according to the following formula S-I:

[Formula S-I]

A- (R ¹ -O) _n- (R ² -O) _{n *} -(R ³ -O) _{n **} -H

(In the above formula,

A is a hydrogenated linear alkyl chain containing 6 to 15 carbon atoms;

R ¹ , R ² and R ³ are each independently an alkoxylation group containing 2 or 3 carbon atoms;

n is an integer from 2 to 100;

n * and n ** are each independently an integer from 0 to 100).

Preferably, A is a hydrogenated linear alkyl chain containing 8 to 15 carbon atoms.

Preferably, n is an integer from 8 to 80.

Preferably, n * and n ** are each independently an integer from 0 to 80.

Mixtures comprising two or more of the above compounds (S) are also included by the present invention.

According to a preferred embodiment, n ** is 0, n * is an integer from 2 to 80, n is an integer from 2 to 50, and R ¹ and R ² identical to each other contain 2 or 3 carbon atoms. It is an alkoxylation group.

According to another embodiment, n * and n ** are both 0, R ¹ is an alkoxylation group containing 2 carbon atoms, and n is an integer from 10 to 80.

According to another embodiment, n and n ** which are identical to each other are integers from 2 to 50, n * is an integer from 10 to 80, and R ¹ and R ^{3 which} are identical to each other include an alkoxylation group containing two carbon atoms. And R ² is an alkoxylation group containing 3 carbon atoms.

According to a preferred embodiment, the compound (S) does not contain secondary alcohol groups. Without being bound by any theory, Applicants have the view that if compound (S) contains one (or more) secondary alcohol groups, the secondary alcohol groups are susceptible to hydrolysis and are therefore not sufficiently stable for electrochemical applications. .

According to a preferred embodiment, the compound (S) is Rhodasurf ^® (available from Solvay Group), Genapol ^® (available from Clariant-Coatings & Construction Chemicals), Empilan ^® KI (available from Huntsman), Lutensol ^® TO and And / or Pluronic ^® (available from BASF), Marlosol ^® TA (available from Sasol Performance Chemicals), and NOVEL ^® TDA-9 (available from Sasol).

A particularly preferred compound (S) is a mixture of compounds of formula SI as detailed above, wherein A is a hydrogenated linear alkyl chain with 13 carbon atoms, R1 is a -CH2-CH2- group, and n * is an average value. This is 7-9, n * and n ** are 0), which can be supplied from different sources under the trade name Marlosol ^® TA3090 or under the trade name NOVEL ^® TDA-9.

Preferably, the polymer (F) comprises repeating units derived from vinylidene fluoride (VDF) and repeating units derived from at least one hydrophilic (meth) acrylic monomer [monomer (MA)].

Preferably, the polymer (F) further comprises a repeating unit derived from VDF and at least one other comonomer (comonomer (C)) different from the monomer (MA).

The comonomer (C) may be a hydrogenated comonomer [comonomer (C _H )] or a fluorinated comonomer [comonomer (C _F )].

In this specification, the term "hydrogenated comonomer [comonomer (C _H )]" is intended to denote an ethylenically unsaturated comonomer free of fluorine atoms.

Non-limiting examples of suitable hydrogenated comonomers (C _H ) include ethylene, propylene, vinyl monomers such as vinyl acetate, as well as styrene monomers such as styrene and p-methylstyrene.

In this specification, the term "fluorinated comonomer [comonomer (C _F )]" is intended to denote an ethylenically unsaturated comonomer comprising at least one fluorine atom.

In a preferred embodiment, the comonomer (C) is a comonomer (C _F ).

Non-limiting examples of suitable fluorinated comonomers (C _F ) include, among others:

(a) C ₂ -C ₈ fluoro- and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;

(b) C ₂ -C ₈ hydrogenated monofluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene;

(c) CH ₂ = CH-R _f0 (where R _f0 is a C ₁ -C ₆ perfluoroalkyl group);

(d) chloro- and / or bromo- and / or iodo-C ₂ -C ₆ fluoroolefins, such as chlorotrifluoroethylene (CTFE);

(e) CF ₂ = CFOR _f1 , where R _f1 is a C ₁ -C ₆ fluoro- or perfluoroalkyl group, for example CF ₃ , C ₂ F ₅ , C ₃ F ₇ ;

(f) CF ₂ = CFOX ₀ (where X ₀ is a C ₁ -C ₁₂ oxyalkyl group, or a C ₁ -C ₁₂ (per) fluorooxyalkyl group having one or more ether groups, for example perfluoro- 2-propoxy-propyl group);

(g) CF ₂ = CFOCF ₂ OR _f2 , where R _f2 is a C ₁ -C ₆ fluoro- or perfluoroalkyl group, for example -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ or A C ₁ -C ₆ (per) fluorooxyalkyl group having one or more ether groups, for example -C ₂ F ₅ -O-CF ₃ );

(h) (per) fluorodioxole of the formula:

(In the above formula, each of R _f3 , R _f4 , R _f5, and R _{f6, which} is the same or different from each other _, is independently a C ₁ -C ₆ fluoro- or per (halo) comprising a fluorine atom, optionally one or more oxygen atoms. ) Fluoroalkyl groups, for example -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ , -OCF ₃ , -OCF ₂ CF ₂ OCF ₃ ).

The most preferred comonomers (C _F ) are tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PMVE) ), Perfluoropropyl vinyl ether (PPVE) and vinyl fluoride.

According to a preferred embodiment, the comonomer (C _F ) is HFP.

When at least one comonomer (C) is present, the polymer (F) is typically 0.05 mol% to 14.5 mol%, preferably 1.0 mol% to 13.0 mol%, relative to the total number of moles of repeat units of the polymer (F). Of, it includes a repeating unit derived from the comonomer (s) (C).

According to this embodiment, the comonomer (C) is preferably selected from comonomers (C _F ) as detailed above, even more preferably HFP.

According to a preferred embodiment, the polymer (F) has an amount of repeating units derived from vinylidene fluoride of at least 85.0 so as not to impair the excellent properties of the vinylidene fluoride resin, such as chemical resistance, weather resistance, and heat resistance. Mol%, preferably at least 86.0 mol%, more preferably at least 87.0 mol%. For example, if the polymer (F) comprises VDF units in an amount of less than 85.0 mol%, the polymer (F) cannot be used to formulate a coating composition for preparing a composite separator for batteries, which corresponds to This is because the polymer to be dissolved will be dissolved in the liquid solvent used as the electrolyte liquid state.

The term “at least one hydrophilic (meth) acrylic monomer [monomer (MA)]” is understood to mean that the polymer (F) may comprise repeating units derived from one or more monomers (MA) as described above. . In the remainder of this specification, the expressions “hydrophilic (meth) acrylic monomer [monomer (MA)]” and “monomer (MA)”, for the purposes of the present invention, in both plural and singular form, ie it is referred to above It is understood that it refers to both one or more hydrophilic (meth) acrylic monomers as defined.

According to a particular embodiment, the polymer (F) consists essentially of repeating units derived from VDF and repeating units derived from said monomer (MA).

According to another embodiment, the polymer (F) consists essentially of repeat units derived from VDF, repeat units derived from HFP and repeat units derived from the monomer (MA).

The polymer (F) may still contain other moieties that do not affect or damage its physical-chemical properties, such as defects, end groups, and the like.

The monomer (MA) preferably follows the formula:

(In the above formula,

Each of R1, R2, R3 which is the same or different from each other is independently a hydrogen atom or a C ₁ -C ₃ hydrocarbon group,

R _OH is a hydroxyl group, or a C ₁ -C ₅ hydrocarbon moiety comprising at least one hydroxyl group).

Non-limiting examples of the monomer (MA) are especially acrylic acid, methacrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxyethylhexyl (meth) acrylate.

The monomer (MA) is more preferably selected from:

-Hydroxyethyl acrylate (HEA) of the formula:

-2-hydroxypropyl acrylate (HPA) of any one of the following formulas:

-Acrylic acid (AA) of the formula:

-And mixtures thereof.

More preferably, the monomer (MA) is AA and / or HEA, even more preferably AA.

Determination of the amount of monomer (MA) repeat units in the polymer (F) can be performed by any suitable method. For example, an acid-base titration method highly suitable for determination of acrylic acid content, an NMR method suitable for quantification of the monomer (MA) (e.g., HPA, HEA) containing aliphatic hydrogen in a side chain, and preparation of a polymer (F) The weight balance based on the total fed monomer (MA) and unreacted residual monomer (MA) during may be particularly mentioned.

Preferably, the polymer (F) comprises at least 0.1 mol%, more preferably at least 0.2 mol%, of repeat units derived from the monomer (MA).

Preferably, the polymer (F) is derived from the monomer (MA), up to 10 mol%, more preferably up to 7.5 mol%, even more preferably up to 5 mol%, most preferably up to 3 mol% It contains repeating units.

Generally, the particles of the polymer (F) have an average primary particle size of less than 1 μm.

For the purposes of the present invention, the term "primary particles" is intended to denote primary particles of polymer (F) derived directly from an aqueous emulsion polymerization process, without isolation of the polymer from the emulsion.

Therefore, the primary particles of the polymer (F) should be intended to be distinguishable from agglomerates (i.e., aggregates of primary particles), which agglomerates by the recovery and conditioning steps of such polymer preparation, such as the polymer (F). ) By concentration and / or coagulation of the aqueous latex, and subsequent drying and homogenization to yield each powder. Thus, the dispersion (D) according to the invention is distinguishable from aqueous slurries which can be prepared by dispersing the powder of the polymer in an aqueous medium. The average particle size of the powder of the polymer or copolymer dispersed in the aqueous slurry is typically greater than 1 μm, as measured according to ISO 13321.

Preferably, the primary particle average size of the particles of the polymer (F) in the dispersion (D) is greater than 20 nm, more preferably greater than 30 nm, even more preferably 50 nm, as measured according to ISO 13321. Is over.

Preferably, the primary particle average size is less than 600 nm, more preferably less than 400 nm and even more preferably less than 350 nm as measured according to ISO 13321.

As mentioned, dispersion (D) is substantially free of fluorinated surfactants.

The expression "substantially free" in combination with the amount of fluorinated surfactant in dispersion (D) should be meant to exclude the presence of any significant amount of the fluorinated surfactant, for example fluorinated surfactant Needs to be present in an amount of less than 5 ppm, preferably less than 3 ppm, more preferably less than 1 ppm, relative to the total weight of the dispersion (D).

The aqueous emulsion polymerization process as detailed above is usually carried out in the presence of at least one radical initiator.

The polymerization pressure is usually in the range of 20 bar to 70 bar, preferably 25 bar to 65 bar.

The choice of the persulfate radical initiator is not particularly limited, but a radical initiator suitable for the aqueous emulsion polymerization process is understood to be selected from compounds capable of initiating and / or accelerating the polymerization process, including sodium persulfate, potassium persulfate and Ammonium persulfate, but is not limited thereto.

One or more radical initiators as defined above may be added to the aqueous medium as defined above, advantageously in an amount ranging from 0.001% to 20% by weight based on the weight of the aqueous medium.

Preferably, the dispersion (D _a ) is subjected to emulsion polymerization by contacting VDF with the at least one monomer (MA), at a pressure of at least 20 bar, at a temperature of up to 80 ° C., in the presence of a persulfate inorganic initiator. Is manufactured through.

Preferably, the emulsion polymerization is carried out in the absence of any fluorinated surfactant (in other words, without adding it).

However, if necessary depending on the circumstances, the dispersion (D _a ) may have an amount of the fluorinated surfactant of less than 5 ppm, preferably less than 3 ppm, more preferably 1 based on the total weight of the dispersion (D _a ). can be prepared to be present in an amount of less than ppm.

The aqueous emulsion polymerization process as detailed above is usually carried out in the presence of at least one radical initiator.

The polymerization pressure is usually in the range of 20 to 70 bar, preferably 25 to 65 bar.

The choice of the persulfate radical initiator is not particularly limited, but a radical initiator suitable for the aqueous emulsion polymerization process is understood to be selected from compounds capable of initiating and / or accelerating the polymerization process, including sodium persulfate, potassium persulfate and Ammonium persulfate, but is not limited thereto.

One or more radical initiators as defined above may be added to the aqueous medium as defined above, advantageously in an amount ranging from 0.001% to 20% by weight based on the weight of the aqueous medium.

Preferably, step (II) is a base selected from ammonia, dimethylethanolamine (DMEA), diethylethanolamine (DEEA), diethanolamine (DEA), triethanolamine (TEA), propyl amine and mixtures thereof. It is done by using.

As described above, in step (II) of contacting the dispersion (D _a ) with at least one base, _a dispersion having a pH of at least 6.5 and less than 9.0, preferably less than 8.7, even more preferably less than 8.5 ( D _b ) is provided.

Surprisingly, the value of the pH in the above range does not substantially adversely affect the properties of the polymer (F), and the polymer (F) has a substantial base-catalyst / base-induced decomposition / defluorination (which results in discoloration and It is very effective in improving the colloidal stability of the dispersions (D _F ) produced from the process of the present invention without exposure to or from contamination, which may result in the release of contaminants such as fluoride ions into the aqueous phase) Turned out.

Preferably, at the end of step (II), a dispersion (D _b ) having a pH of 6.5 to 8.7, preferably 6.5 to 8.5, even more preferably 7 to 8 is provided.

A pH value of 9 or higher should be avoided because it has been found to surprisingly cause discoloration of the polymer (F) and generation of significant amounts of fluoride ions due to the hydrofluorination side reactions occurring on the VDF-derived repeat units of the polymer (F), This can adversely affect the performance of the dispersion (D _F ) for use as intended.

Advantageously, the pH of the final dispersion (D _F ) is not adversely affected by the addition of compound (S), that is, the pH of the dispersion (D _b ) and the dispersion (D _F ) is consistent.

Advantageously, the dispersion (D _F ) is used to provide a coating on a separator for an electrochemical cell.

Aqueous coating compositions suitable for coating separators can be obtained by adding and dispersing non-electroactive inorganic filler materials, and optional additives into the dispersion (D _F ).

Accordingly, another object of the present invention is an aqueous coating composition [composition (composition (()) comprising a dispersion (D _F ) as described in detail above, at least one non-electroactive inorganic filler material, and, optionally, one or more additional additives. AC)].

In this specification, the term “non-electroactive inorganic filler material” is intended to denote an electrically non-conductive inorganic filler material suitable for the manufacture of an electrically insulating separator for an electrochemical cell.

The non-electroactive inorganic filler material in the separator according to the invention typically has an electrical resistivity (p) of at least 0.1 × 10 ¹⁰ ohm cm, preferably at least 0.1 × 10 ¹² when measured at 20 ° C. according to ASTM D 257. ohm cm.

Non-limiting examples of suitable non-electroactive inorganic filler materials include, among others, natural and synthetic silica, zeolites, alumina, titania, metal carbonates, zirconia, silicon phosphates and silicates, and the like.

Non-electroactive inorganic filler materials, when measured according to ISO 13321, are typically in the form of particles having an average size of 0.01 μm to 50 μm.

Optional additives in the composition (AC) include viscosity modifiers, antifoaming agents, non-fluorinated surfactants, and the like as described above in detail.

Among the non-fluorinated surfactants, nonionic emulsifiers, such as alkoxylated alcohols, for example, ethoxylated alcohols, propoxylated alcohols, mixed ethoxylated / propoxylated alcohols; Anionic surfactants such as fatty acid salts, alkyl sulfonate salts (eg sodium dodecyl sulfate), alkylaryl sulfonate salts, arylalkyl sulfonate salts and the like can be mentioned.

The composition (AC) can be obtained from the dispersion (D _F ), for example, by a method comprising one of the following:

(i) formulating the dispersion (D _F ) with optional additives as detailed above; or

(ii) up-concentrating the dispersion (D _F ), in particular through standard techniques such as ultrafiltration, clouding, etc .; or

(iii) using the dispersion (D _F ) as obtained from emulsion polymerization; or

(iv) by diluting the dispersion (D _F ) with water, or through a combination of the above techniques.

Generally, the composition (AC) is:

(i) a dispersion as detailed above (D _F ) in an amount of 5% to 25% by weight;

(ii) at least one non-electroactive inorganic filler material in an amount of 70% to 95% by weight;

(iii) one or more additional additives in an amount of 0% to 5% by weight

Mix;

(iv) Optionally obtained by adding water to adjust the solids content in the range of 30% to 80% by weight, preferably 40% to 60% by weight.

It is understood that the solids content of the composition (AC) is a cumulative total of all its non-volatile components, especially including the polymer (F) and non-electroactive inorganic filler materials.

Another object of the present invention is a method for producing a composite separator particularly suitable for use in an electrochemical cell, the method comprising the following steps:

(1) providing a porous substrate having at least one surface;

(2) an aqueous coating composition comprising the dispersion (D _F ), at least one non-electroactive inorganic filler material, and, optionally, at least one additional additive, i.e., a composition (AC) as detailed above. Providing;

(3) applying the composition (AC) on at least one surface of the porous substrate to provide a coating composition layer; And

(4) providing the composite separator by drying the coating composition layer at a temperature of at least 60 ° C.

As used herein, the term "separator" is intended to denote electrically porous and porous polymer materials that electrically and physically separate electrodes of opposite polarity in an electrochemical cell and are ions flowing between them.

As used herein, the term “electrochemical cell” is intended to denote an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein a single layer or multilayer separator is adhered to at least one surface of one of the electrodes.

Non-limiting examples of electrochemical cells include, in particular, batteries, preferably secondary batteries, and electric double layer capacitors.

For the purposes of the present invention, "secondary battery" is intended to denote a rechargeable battery. Non-limiting examples of secondary batteries include, inter alia, alkali or alkaline-earth secondary batteries, more preferably lithium batteries.

The composite separator obtained from the method of the present invention is advantageously an electrically insulating composite separator suitable for use in electrochemical cells.

In step (3) of the method of the present invention, the composition (AC) is typically cast, spray coating, roll coating, doctor blading, slot die coating, gravure coating, inkjet printing, spin coating and screen printing, brush, It is applied on at least one surface of the porous substrate by a technique selected from squeegees, foam applicators, curtain coatings, and vacuum coatings.

Non-limiting examples of suitable porous substrates include, in particular, porous membranes made from inorganic, organic and naturally occurring materials, specifically nonwoven fibers (cotton, polyamide, polyester, glass), polymers (polyethylene, polypropylene, poly ( Porous membranes made of tetrafluoroethylene), poly (vinyl chloride), and certain fibrous naturally occurring materials (eg asbestos).

Advantageous results have been obtained when the porous support is a polyolefin porous support, for example a polyethylene or polypropylene porous support.

In step (4) of the method of the invention, the coating composition layer is preferably dried at a temperature comprised between 60 ° C and 200 ° C, preferably between 70 ° C and 180 ° C.

In addition to the above, the aqueous electrode-forming composition adds a powdered electrode material (active material for battery or electric double layer capacitor), and optional additives, such as an electroconductive-imparting additive and / or a viscosity modifier into the dispersion (D _F ). And dispersion.

Accordingly, also an object of the present invention is an aqueous electrode-forming composition comprising a dispersion (D _F ) as described in detail above, a powdered electrode material, and optionally, an electroconductive-imparting additive and / or a viscosity modifier.

Among the viscosity modifiers, a thickener can be added to prevent or slow down sedimentation of the powdered electrode material from the aqueous composition of the present invention. Non-limiting examples of suitable thickeners include in particular organic thickeners such as partially neutralized poly (acrylic acid) or poly (methacrylic acid), carboxylated alkyl celluloses such as carboxylated methyl cellulose and inorganic thickeners such as natural clays ( clay), such as montmorillonite and bentonite, artificial clay, such as laponite and others, such as silica and talc.

In the case of forming a positive electrode for a lithium ion battery, the active material may include a complex metal chalcogenide represented by the general formula LiMY ₂ , where M is at least one chemical species of the transition metal, such as Co, Ni, Fe, Mn , Cr and V; Y represents a chalcogen, such as O or S. Among them, it is preferable to use a lithium-based composite metal oxide represented by the general formula LiMO ₂ , where M is the same as above. Preferred examples thereof may include: LiCoO ₂ , LiNiO ₂ , LiNi _x Co _1-x O ₂ (0 <x <1), and spinel-structure LiMn ₂ O ₄ .

In the case of forming a negative electrode for a lithium battery, the active material may preferably include a carbonaceous material, such as graphite, activated carbon, or a carbonaceous material obtained by carbonization such as phenolic resin or pitch. The carbonaceous material may preferably be used in the form of particles having an average diameter of about 0.5 to 100 μm.

In order to improve the conductivity of the resulting composite electrode layer formed by applying and drying the electrode-forming composition of the present invention, an electroconductive-imparting additive may be added, in particular, an active material exhibiting limited electron-conductivity, such as LiCoO ₂ This is the case when using. Examples of electroconductive-imparting additives may include: carbonaceous materials such as carbon black, graphite fine powders and fibers, and fine powders and fibers of metals such as nickel and aluminum.

The active material for electric double layer capacitors preferably has an average particle (or fiber) diameter of 0.05 to 100 μm and a specific surface area of 100 to 3000 m ² / g, that is, relatively small particles (or fibers) compared to the active material for batteries. Microparticles or fibers having a diameter and a relatively large specific surface area, such as activated carbon, activated carbon fibers, silica or alumina particles.

Preferred electrode-forming compositions for positive electrodes include:

(a) polymer present in an amount of 1 to 10% by weight, preferably 2 to 9% by weight, more preferably about 3% by weight relative to the total weight of component (a) + (b) + (c) (F);

(b) electricity present in an amount of 2 to 10% by weight, preferably 4 to 6% by weight, more preferably about 5% by weight relative to the total weight of component (a) + (b) + (c) Carbon black as a conductive-imparting additive;

(c) a powdered electrode material, preferably in the general formula LiMY ₂ as detailed above, present in an amount of 80 to 97% by weight, preferably 85 to 94% by weight, more preferably about 92% by weight. Composite metal chalcogenide shown.

Now, the present invention will be described in more detail with reference to the following examples, and the purpose of the following examples is merely illustrative and does not limit the scope of the invention.

Experiment section

material

Pluronic ^® F108: a block copolymer surfactant (CAS No. 9003-11-6) of the formula PEG-PPG-PEG were purchased from Sigma-Aldrich.

Marlosol ^® TA3090 : Isotridecanol ethoxylate C ₁₃ (CAS No. 69011-36-5) was obtained by BRENNTAG AG.

Synthesis 1-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer A1)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 80 ° C. and the pressure of 35 Bar ass was kept constant throughout the entire test by feeding a gaseous mixture monomer of VDF / HFP in a 99: 1 molar ratio each.

250 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 15 minutes (1 L / h), followed by 60 ml of ammonium persulfate (APS) solution for the entire duration of this test. continued addition at a flux rate of / h; In addition, 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) was fed every 250 g of consumed monomer.

When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 223 minutes. The reactor was cooled to room temperature, and latex was recovered.

The VDF-HFP-AA polymer thus obtained contained 98.3 mol% of VDF, about 1.0 mol% of HFP and 0.7 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 24.8% by weight.

The VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 243 nm, as measured according to ISO 13321, has a melting point of 153.6 ° C. (determined according to ASTM D3418) and MV (230 ° C. / 100 sec ^-1 ) is 67 kP and the content of end groups was found to be as follows: -CF ₂ H: 35 mmol / kg; -CF ₂ -CH ₃ : 19 mmol / kg; -CH ₂ OH: 8 mmol / kg.

Synthesis 2-Preparation of aqueous VDF-AA polymer dispersion (Polymer A2)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was set to 90 ° C, and the pressure of 20 Bar Ass was kept constant throughout the entire test by supplying the VDF gas phase monomer. 15 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 5 minutes (200 ml / h) and at the same time 22 ml of acrylic acid (AA) solution (40 g / l acrylic acid in water) ) Was fed every 225 g of polymer to be synthesized. After 30 minutes, an additional amount of APS solution was added at a flow rate of 240 ml / h for the entire duration of this test.

When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 164 minutes.

The reactor was cooled to room temperature, and latex was recovered. The VDF-AA polymer thus obtained contained 99.55 mol% of VDF and 0.45 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 24.2% by weight.

VDF-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 189 nm, as measured according to ISO 13321, has a melting point of 160 ° C. (determined according to ASTM D3418) and MV (230 ° C./100 sec It was confirmed that ^-1 ) was 23 kP.

Synthesis 3-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer B1)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 75 ° C., and the pressure of 35 Bar Ass was kept constant throughout the entire test by supplying a gas phase mixture monomer of 99: 3 molar ratio VDF / HFP each. 290 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 17 minutes (1 L / h), and then the APS solution was added at a flow rate of 60 ml / h for the entire duration of this test. Supplied; A 50 ml acrylic acid (AA) solution (50 g / l acrylic acid in water) was fed every 250 g of spent monomer.

When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 318 minutes.

The reactor was cooled to room temperature and the latex was unloaded.

The VDF-HFP-AA polymer thus obtained contained 96.13 mol% of VDF, 2.97 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 24.0% by weight.

The VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 287 nm, as measured according to ISO 13321, has a melting point of 144 ° C. (determined according to ASTM D3418), MV (230 ° C. / 100 sec ^-1 ) was 31 kP and the content of the end groups was found to be as follows: -CF ₂ H: 35 mmol / kg; -CF ₂ -CH ₃ : 23 mmol / kg; -CH ₂ OH: 5 mmol / kg.

Synthesis 4-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer B2)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 90 ° C., and the pressure of 30 Bar Ass was kept constant throughout the entire test by supplying a gas phase mixture monomer of 99: 3 molar ratio of VDF / HFP, respectively. 250 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 15 minutes (1 L / h), and at the same time 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) ) Was fed every 250 g of polymer to be synthesized.

After 30 minutes, the APS solution was fed at a flow rate of 240 ml / h for the entire duration of this test. When the 4500 g mixture was supplied, the supply of the mixture was stopped, and the pressure was allowed to drop to a maximum of 12 bar while maintaining the reaction temperature constant. The final reaction time was 125 minutes. The reactor was cooled to room temperature, and latex was recovered.

The VDF-HFP-AA polymer thus obtained contained 96.13 mol% of VDF, 2.97 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 25.4% by weight.

VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles with an average primary size of 220 nm, as measured according to ISO 13321, has a melting point of 141 ° C. (determined according to ASTM D3418), MV (230 ° C. / 100 sec ^-1 ) was 22 kP.

Synthesis 5-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer C1)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 75 ° C., and then HFP gas phase monomer was charged until a delta P of 6.1 bar was achieved. The pressure of 35 bar was kept constant throughout the entire test by feeding the gaseous mixture monomers of 87.5: 12.5 molar ratios of VDF / HFP each. 250 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 15 minutes (1 L / h), followed by 60 ml of ammonium persulfate (APS) solution for the entire duration of this test. Continued addition at a flow rate of / h, with which 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) was fed every 250 g of the synthesized polymer.

When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 326 minutes.

The reactor was cooled to room temperature and the latex was unloaded.

The VDF-HFP-AA polymer so obtained contained 86.72 mol% of VDF, 12.38 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer. The aqueous latex thus obtained had a solids content of 25.6% by weight.

VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles with an average primary size of 273 nm, as measured according to ISO 13321, has a melting point of 89 ° C. (determined according to ASTM D3418), MV (230 ° C. / 100 sec ^-1 ) was 48.6 kP, and the content of the end groups was found to be as follows: -CF ₂ H: 29 mmol / kg; -CF ₂ -CH ₃ : 10 mmol / kg; -CH ₂ OH: 7 mmol / kg.

Synthesis 6-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer C2)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 90 ° C., and the pressure of 30 Bar was kept constant throughout the entire test by feeding a gaseous mixture monomer of 87.5: 12.5 molar ratio of VDF / HFP each. 250 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 15 minutes (1 L / h), and at the same time 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) ) Was fed every 250 g of polymer to be synthesized.

After 30 minutes from ignition, the addition of the ammonium persulfate (APS) solution at a flow rate of 240 ml / h for the entire duration of this test was restarted. When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 141 minutes. The reactor was cooled to room temperature and the latex was unloaded.

The VDF-HFP-AA polymer so obtained contained 86.7 mol% of VDF, 12.4 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer. The aqueous latex thus obtained had a solids content of 23.8% by weight.

The VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 340 nm, as measured according to ISO 13321, has a melting point of 81.2 ° C. (determined according to ASTM D3418), MV (230 ° C. / 100 sec ^-1 ) was 14 kP.

Synthesis 7-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer D1)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 90 ° C., and then HFP gas phase monomer was charged until a delta P of 10.6 bar was achieved. The pressure of 35 bar was kept constant throughout the entire test by feeding the gaseous mixture monomers of VDF / HFP in a molar ratio of 78.5: 21.5 each.

220 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 13 minutes (1 L / h), followed by 60 ml of ammonium persulfate (APS) solution for the entire duration of this test. Continued addition at a flow rate of / h, with which 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) was fed every 250 g of the synthesized polymer.

After 450 g conversion, the polymerization temperature was lowered to 75 ° C. When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 269 minutes. The reactor was cooled to room temperature and the latex was unloaded.

The VDF-HFP-AA polymer thus obtained contained 77.8 mol% of VDF, 21.3 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 25.7% by weight.

The VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 292 nm, as measured according to ISO 13321, has a Tg of -21.1 ° C (determined according to ASTM D3418) and MV (230 ° C) / 100 sec ^-1 ) is 40 kP, Mooney ((1 + 10 ') at 121 ° C) is 158.1, and the content of end groups was found to be as follows: -CF ₂ H: 25 mmol / kg; -CF ₂ -CH ₃ : 37 mmol / kg; -CH ₂ OH: 7 mmol / kg.

Synthesis 8-Preparation of aqueous VDF-HFP-AA polymer dispersion (Polymer D2)

To a 21 liter horizontal reactor autoclave equipped with a stirrer and baffle operated at 50 rpm, 13.5 liters of deionized water was introduced. The temperature was brought to 90 ° C., and then HFP gas phase monomer was charged until a delta P of 8.8 bar was achieved. The pressure of 30 Bar Ass was kept constant throughout the entire test by feeding the gaseous mixture monomer of VDF / HFP in a molar ratio of 78.5: 21.5 each. 250 ml of ammonium persulfate (APS) aqueous solution (100 g / l) was added over a period of 15 minutes (1 L / h), and at the same time 50 ml of acrylic acid (AA) solution (50 g / l acrylic acid in water) ) Was fed every 250 g of polymer to be synthesized.

After 30 minutes from ignition, the addition of the ammonium persulfate (APS) solution at a flow rate of 240 ml / h for the entire duration of this test was restarted. When 4500 g of the mixture was fed, the feed of the mixture was stopped, and then the pressure was allowed to drop to a maximum of 12 bar while keeping the reaction temperature constant. The final reaction time was 285 minutes. The reactor was cooled to room temperature and the latex was unloaded.

The VDF-HFP-AA polymer thus obtained contained 77.8 mol% of VDF, 21.3 mol% of HFP and 0.9 mol% of acrylic acid (AA) monomer.

The aqueous latex thus obtained had a solids content of 24% by weight.

As measured according to ISO 13321, VDF-HFP-AA polymer dispersed in aqueous latex, in the form of particles having an average primary size of 285 nm, has a Tg of -15.9 ° C (determined according to ASTM D3418) and MV (230 ° C) / 100 sec ^-1 ) was 23 kP, Mooney ((1 + 10 ') at 121 ° C. was 63.3), and the content of end groups was found to be as follows: -CF ₂ H: 68 mmol / kg; -CF ₂ -CH ₃ : 15 mmol / kg; -CH ₂ OH: 38 mmol / kg.

The properties of the latexes prepared according to Examples 1-8 are summarized in Table 1 below.

synthesis polymer VDF / HFP Mall: Mall T _m (℃) MV (kP) (at 100 sec ^-1 ) Example 1 A1 99: 1 153.6 67 Example 2 A2 100: 0 160.0 23 Example 3 B1 97: 3 144.0 31 Example 4 B2 97: 3 140.0 22 Example 5 C1 87.5: 12.5 89.0 49 Example 6 C2 87.5: 12.5 81.2 14 Example 7 D1 78.5: 21.5 (*) T _g = -21.1 40 Example 8 D2 78.5: 21.5 (*) T _g = -15.9 23

(*): No detectable melting point

Preparation of latex 1A

18.4 Kg of 25.5 wt% polymer A2 (pH = 2.4 at the end of polymerization) was discharged from the polymerization reactor into a 40 L glass reactor equipped with a baffle and a mechanical stirrer set at 250 rpm.

Ammonia solution (40 ml, 29% by weight) was added dropwise until the final pH reached 7.5 to adjust the pH.

Keeping the latex under stirring, and the 3300 g Pluronic ^® F-108 solution diluted with deionized water to 10% by weight was added to 135 minutes to 25 ml / min.

The solids content at the end of stabilization was 21.6% by weight.

Thus, latex 1A is contained Pluronic ^® F-108 in an amount of 1.8% by weight based on the total weight of latex 1A.

Preparation of latex 1B

Except a solution of 1830 g of Pluronic ^® F-108 was diluted with deionized water to 10% by weight of the addition to 25 ml / min, according to the same procedure as described above for Latex 1 was prepared latex 1B.

Thus, latex 1B is contained Pluronic ^® F-108 in an amount of 1% by weight, based on the total weight of latex 1B.

Preparation of latex 2

19.5 Kg of 25 wt% polymer B2 (pH = 2.0 at the end of polymerization) was discharged from the polymerization reactor into a 40 L glass reactor equipped with a baffle and a mechanical stirrer set at 250 rpm.

The pH was adjusted by dropping ammonia solution (44 ml, 29% by weight) until the final pH was 7.1.

Keeping the latex under stirring, a solution of 1403 g Marlosol ^® TA3090 diluted with deionized water to 25% by weight to about 10 ml / min was added to 120 minutes.

The solids content at the end of stabilization was 23.9% by weight.

Thus, latex 2 is contained Marlosol ^® TA3090 in an amount of 1.5% by weight, based on the total weight of latex 2.

Preparation of latex 3

18.2 Kg of 25.5 wt% polymer A2 (pH = 2.4 at the end of polymerization) was discharged from the polymerization reactor into a 40 L glass reactor equipped with a baffle and a mechanical stirrer set at 250 rpm.

The pH was adjusted by dropping ammonia solution (40 ml, 29 wt%) until the final pH was 7.35.

Keeping the latex under stirring, a solution of 1093 g TA3090 Marlosol ^® diluted with deionized water to 25% by weight to about 13 ml / min was added to the 85 minutes.

The solids content at the end of stabilization was 23.6% by weight.

Thus, latex 3 is contained Marlosol ^® TA3090 in an amount of 1.5% by weight, based on the total weight of the latex 3.

Preparation of concentrated latex

The latex 2 and latex 3 prepared as described above were circulated through an ultrafiltration unit consisting of a tubular ultrafiltration filter bundle via a peristaltic pump, where the liquid aqueous phase was removed until the following solids content was reached:

-For 2U latex, 53.6% by weight of solids content, 2.56% by weight of residual Marlosol ^® TA 3090; And

-For 3U latex, 52.7% by weight of solids content, 2.54% by weight of residual Marlosol ^® TA 3090.

Example 1-Accelerated test by a climate chamber at 37 ° C

Each 0.5 L of latex 1-3 prepared as described above was closed in a glass bottle and stored in a climate chamber set at 37 ° C.

Method (A)

Evaluation of the solids content was performed using a thermal balance (Mod Crystal Therm-Gibertini). Once a week, after gently shaking the bottle, a portion of each latex was taken out and heated to 180 ° C. The amount of water left was a measure of the final percentage of solids content.

Method (B)

Each month, after gently shaking each latex, a portion of each latex was taken out and the diameter of the particles was evaluated by light scattering technique.

The results obtained for Polymer A2 and Polymer B2 are reported in Tables 2-4 below.

As a comparison, the following latex was prepared by adding a surfactant to the polymer as obtained at the end of the polymerization reaction, i.e., without pH adjustment:

- a pH = 2, C1 latex containing polymer A2 + 1 wt% Pluronic ^® F-108;

-latex C2 with pH = 2 and comprising polymer B2 alone;

- a pH = 2, C3 latex containing polymer B2 + 1.5 wt% Marlosol ^® TA3090.

Days Latex C1 ( ^* ) Latex 1B Latex 1A S.C.% dp (nm) S.C.% dp (nm) S.C.% dp (nm) 3 22.87 296 22.87 296 21.62 296 10 22.66 n / p 22.67 n / p 21.48 n / p 45 20.48 348 22.71 n / p 21.88 n / p 50 Solidified 22.63 305 21.83 324 100 - 22.52 315 21.69 290 150 - 22.06 303 20.73 300 200 - 18.89 294 20.23 300

( ^* ) Comparison

S.C. = Solids content

dp = particle diameter

n / p = not performed

Days Latex C2 ( ^* ) Latex C3 ( ^* ) Latex 2 S.C.% dp (nm) S.C.% dp (nm) S.C.% dp (nm) 6 25.01 220 23.95 220 24.0 220 20 25.46 n / p 24.21 n / p n / p n / p 55 22.7 248 25.0 236 25.52 216 62 Solidified 25.03 238 25.42 220 100 - 24.62 265 25.45 223 132 - 7.91 365 25.35 223 150 - Solidified 24.48 222 200 - - 24.96 230

( ^* ) Comparison

S.C. = Solids content

dp = particle diameter

n / p = not performed

Days Latex 3U Latex 2U S.C.% dp (nm) S.C.% dp (nm) 10 53.64 240 52.76 220 50 53.30 247 52.03 237 100 52.52 254 52.12 250 150 52.52 249 52.68 241 170 39.03 n / p 52.35 241

S.C. = Solids content

dp = particle diameter

n / p = not performed

Effect of various adjusted pH in step (II) starting from latex of polymers A2 and B2

Three latex samples, each having a weight of 0.5 Kg and containing 23.39% by weight of polymer A2, were obtained from polymer A2 latex, wherein polymer A2 latex was obtained by polymerization as described above, at the end of polymerization the pH was 2.12. It was.

The first sample was polymerized as polymer A2 latex without ammonia added. In the second sample, the ammonia solution was added dropwise under stirring to adjust the pH until the final pH was 6.9 (3 ml of 29% vol / vol ammonia aqueous solution was added); In the third sample, the pH was adjusted in a similar manner to a value of 9.01 (9.5 ml of 29% v aqueous ammonia solution was added). To provide a meaningful fluoride concentration determination, water was added to the three samples to ensure the exact same final volume.

Similarly, three latex samples, each weighing 0.5 Kg and containing 24.43% by weight polymer B2, were obtained from polymer B2 latex, where polymer B2 latex was obtained by polymerization as described above, at the end of polymerization The pH was 2.31.

The first sample was polymerized as polymer B2 latex without ammonia added. In the second sample, the ammonia solution was added dropwise under stirring to a final pH of 7.0 (4.5 ml of 29% vol / vol ammonia aqueous solution added) and 9.02 (13 ml of 29% vol / vol ammonia aqueous solution added). The pH was adjusted until. To provide a meaningful fluoride concentration determination and to maintain substantially the same solids content, water was added to the three samples to ensure the exact same final volume.

Different samples were examined for their color properties after 12 hours; Cryogenic coagulation was applied to the specimens of each sample, the supernatant aqueous phase was centrifuged at 10,000 rpm for 10 minutes, diluted 1:50, and then subjected to liquid ion chromatography for fluoride quantification. The results are collected in the table below.

The color test results as detailed below were performed by comparing the coagulated polymers, where 'white' represents a product that does not have a distinctive color shade, and 'yellowish' is clearly deviated from an off-white shade. Product.

Sample Adjusted pH Polymer color Fluoride
From latex of polymer A2 As it is (pH = 2.12) White 215 Adjusted to pH = 6.90 White 250 Adjusted to pH = 9.01 Yellowish 275 From latex of polymer B2 As it is (pH = 2.31) White 225 Adjusted to pH = 7.0 White 260 Adjusted to pH = 9.02 Yellowish 285

The results summarized below well confirm the importance of selecting the proper pH in adjusting the pH in step (II) of the method of the present invention.

Claims (15)

A method for stabilizing an aqueous dispersion (dispersion (D _a )) comprising particles of a (semi) crystalline VDF-based polymer [polymer (F)] comprising the following steps:
(I) providing the dispersion (D _a );
(II) contacting the dispersion (D _a ) with at least one base to provide a VDF-based (semi) crystalline polymer aqueous dispersion having a pH above 6.5 and below 9.0 (dispersion (D _b )). ;
(III) The dispersion (D _b ) obtained in step (II) comprises a hydrogenated linear alkyl chain containing 6 to 15 carbon atoms and a (poly) alkoxylation group containing 2 or 3 carbon atoms. Contacting at least one nonionic surfactant (compound (S)) to provide a stabilized aqueous dispersion [dispersion (D _F )]. The method according to claim 1, wherein the compound (S) is according to the following formula SI:
[Formula SI]
A- (R ¹ -O) _n- (R ² -O) _{n *} -(R ³ -O) _{n **} -H
(In the above formula,
A is a hydrogenated linear alkyl chain containing 6 to 15 carbon atoms;
R ¹ , R ² and R ³ are each independently an alkoxylation group containing 2 or 3 carbon atoms;
n is an integer from 2 to 100;
n * and n ** are each independently an integer from 0 to 100). According to claim 2, In the formula SI,
-n ** is 0, n * is an integer from 2 to 80, n is an integer from 2 to 50, and R ¹ and R ^{2 which} are identical to each other are alkoxylated groups containing 2 or 3 carbon atoms;
-n * and n ** are both 0, R ¹ is an alkoxylation group containing 2 carbon atoms, n is an integer from 10 to 80;
-N and n **, which are identical to each other, are integers of 2 to 50, n * is an integer of 10 to 80, and R ¹ and R ^{3 which} are identical to each other are alkoxylation groups containing 2 carbon atoms, and R ² is 3 Method, which is an alkoxylated group containing two carbon atoms. The method according to any one of claims 1 to 3, wherein compound (S) is a mixture of two or more compounds (S) as defined in claim 2 or 3. The polymer (F) is a repeating unit derived from vinylidene fluoride (VDF), derived from at least one hydrophilic (meth) acrylic monomer [monomer (MA)]. A repeating unit, and, optionally, a repeating unit derived from VDF and at least one other comonomer (comonomer (C)) different from the monomer (MA). The method of claim 5, wherein the comonomer (C) is selected from:
-Hydrogenated comonomer [comonomer (C _H )], more preferably a comonomer selected from the group comprising ethylene, propylene, vinyl monomers such as vinyl acetate, as well as styrene monomers such as styrene and p-methylstyrene ( C _H ); or
-A fluorinated comonomer [comonomer (C _F )], more preferably a comonomer (C _F ) selected from the group comprising:
(a) C ₂ -C ₈ fluoro- and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;
(b) C ₂ -C ₈ hydrogenated monofluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene;
(c) CH ₂ = CH-R _f0 (where R _f0 is a C ₁ -C ₆ perfluoroalkyl group);
(d) chloro- and / or bromo- and / or iodo-C ₂ -C ₆ fluoroolefins, such as chlorotrifluoroethylene (CTFE);
(e) CF ₂ = CFOR _f1 , where R _f1 is a C ₁ -C ₆ fluoro- or perfluoroalkyl group, for example -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ ;
(f) CF ₂ = CFOX ₀ (where X ₀ is a C ₁ -C ₁₂ oxyalkyl group, or a C ₁ -C ₁₂ (per) fluorooxyalkyl group having one or more ether groups, for example perfluoro- 2-propoxy-propyl group);
(g) CF ₂ = CFOCF ₂ OR _f2 , where R _f2 is a C ₁ -C ₆ fluoro- or perfluoroalkyl group, for example -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ or A C ₁ -C ₆ (per) fluorooxyalkyl group having one or more ether groups, for example -C ₂ F ₅ -O-CF ₃ );
(h) (per) fluorodioxole of the formula:

(In the above formula, each of R _f3 , R _f4 , R _f5 , and R _{f6, which} is the same or different from each other, is independently a C ₁ -C ₆ fluoro- or per (halo) containing a fluorine atom, optionally one or more oxygen atoms. ) Fluoroalkyl groups, for example -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ , -OCF ₃ , -OCF ₂ CF ₂ OCF ₃ ). The method of claim 6, wherein the comonomer (C _F ) is tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluoro A method comprising, more preferably selected from the group consisting of methyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE) and vinyl fluoride. The method according to claim 5, wherein the monomer (MA) is according to the following formula:

(In the above formula,
Each of R1, R2, R3 which is the same or different from each other is independently a hydrogen atom or a C ₁ -C ₃ hydrocarbon group,
R _OH is a hydroxyl group, or a C ₁ -C ₅ hydrocarbon moiety comprising at least one hydroxyl group). The method of claim 8, wherein the monomer (MA) comprises acrylic acid, methacrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxyethylhexyl (meth) -acrylate Method selected from the group. The method of claim 1, wherein the average size of the particles of the polymer (F) is greater than 20 nm, more preferably greater than 30 nm, even more preferably greater than 50 nm, as measured according to ISO 13321; And / or less than 600 nm, more preferably less than 400 nm, even more preferably less than 350 nm. The dispersion (D _b ) according to claim 1, wherein at the end of step (II), the pH is 6.5 to 8.7, preferably 6.5 to 8.5, even more preferably 7 to 8. ) Is provided, how. An aqueous coating composition comprising a dispersion (D _F ) as defined in any one of claims 1 to 11, at least one non-electroactive inorganic filler material, and optionally, one or more additional additives. [Composition (AC)]. A method of making a composite separator particularly suitable for use in an electrochemical cell comprising the following steps:
(1) providing a porous substrate having at least one surface;
(2) providing a composition (AC) according to claim 12;
(3) applying the composition (AC) on at least one surface of the porous substrate to provide a coating composition layer; And
(4) providing the composite separator by drying the coating composition layer at a temperature of at least 60 ° C. 14. The porous substrate according to claim 13, wherein the porous substrate is a porous membrane made from inorganic, organic and naturally occurring materials, specifically nonwoven fibers (cotton, polyamide, polyester, glass), polymers (polyethylene, polypropylene, poly (tetra) Fluoroethylene), poly (vinyl chloride), and porous membranes made from certain fibrous naturally occurring materials (eg asbestos). Aqueous electrode-forming, comprising a dispersion (D _F ) as defined in any one of claims 1 to 11, a powdered electrode material, and, optionally, an electroconductive-imparting additive and / or a viscosity modifier. Composition.